1. Field of the Invention
This invention relates to a blade driving apparatus for cameras designed so that blades, such as shutter blades or stop blades, are driven by an electromagnetic actuator.
2. Description of Related Art
Each of lens shutter apparatuses (hereinafter referred to as shutter apparatuses), stop apparatuses, filter apparatuses, and lens barrier apparatuses which are used in recent cameras has a single blade or a plurality of blades so that they are reciprocated by an electromagnetic actuator. As is well known, each of these apparatuses may be unified by itself, but two or three of them may be constructed as one unit.
The shutter apparatuses are generally designed so that two shutter blades are reciprocated and rotated simultaneously in opposite directions. However, some of the shutter apparatuses may be constructed so that a single shutter blade is reciprocated and rotated. It is also known that at least one of the two shutter blades reciprocated and rotated simultaneously in opposite directions is constructed with two divided blade components so that when the shutter is fully opened, these blade components are completely superimposed, and thereby less space for incorporating the shutters is required and compactness of the apparatus is achieved. It is further known that the shutter apparatus designed as mentioned above can be constructed as a lens barrier apparatus by arranging the blades in front of a photographic lens.
In the stop apparatuses, it is common practice to use a stop ring so as to reciprocate and rotate a plurality of stop blades simultaneously in the same direction. However, in recent small-sized digital cameras including cameras for incorporating information terminals such as mobile phones and PDAs (personal digital assistants), it is general practice to reciprocate and rotate a single stop blade that has a small circular aperture section. In recent filter apparatuses, it is common practice to cover the aperture section configured in the above single stop blade with an ND filter plate as a filter blade.
For the electromagnetic actuator, a step motor may be used, but when the apparatus is small in size, it is standard practice to use a current-controlled electromagnetic actuator. This electromagnetic actuator is such that a rotor made with a permanent magnet is turned in a direction according to the conductive direction of a stator coil and the blades are reciprocated by its output pin. The electromagnetic actuators used at present are roughly divided into two types, depending on the structure of the stator. The first type electromagnetic actuator is such that the stator coil is wound around a stator frame incorporating the rotor so as to surround two bearing portions of the rotor. The second type electromagnetic actuator is such that the stator coil is wound around a nearly U-shaped yoke. The second type electromagnetic actuator is suitable for the slim design of the entire apparatus.
Although the present invention relates to a blade driving apparatus for cameras adopting the second type electromagnetic actuator, of the current-controlled electromagnetic actuators mentioned above, Japanese Patent Kokai No. 2005-156616 discloses an apparatus in which the electromagnetic actuator of the above structure is adopted and the shutter apparatus and the stop apparatus are constructed as one unit.
However, the blade driving apparatus set forth in Kokai No. 2005-156616 has the following structure (words in parenthesis described below are names and reference numerals of members used in Kokai No. 2005-156616). A blade chamber is provided between a base plate (a base plate 1) and a partition plate (a partition plate 6) made with a thin material, and cover frames (bobbin members 7 and 12) are mounted to the base plate (the base plate 1) at the side position of an exposure aperture so that the partition plate (the partition plate 6) is interposed between the base plate and the cover frames. Although yokes (yokes 9, 10, 14, and 15) are interposed between the partition plate (the partition plate 6) and the cover frames (the bobbin members 7 and 12), permanent magnet rotors (permanent magnet rotors 2 and 3) are interposed between the base plate (the base plate 1) and the cover frames (the bobbin members 7 and 12). Such an arrangement is advantageous for the compact and slim design of the blade driving apparatus, and thus is extremely favorable for use not only in a single camera, but also in a camera incorporating an information terminal, such as a mobile phone or PDA, or an in-vehicle camera.
However, this arrangement, although favorable for the slim design of the apparatus, is not necessarily be favorable in the case where the area of the base plate (the base plate 1) is reduced to achieve compactness of the apparatus. This is because the permanent magnet rotors (the permanent magnet rotors 2 and 3) are interposed between the base plate (the base plate 1) and the cover frames (the bobbin members 7 and 12) and hence when an attempt is made to reduce the area of the base plate (the base plate 1), blades (a stop blade 4 and a shutter blade 5) must be prevented from interfering with the permanent magnet rotors (the permanent magnet rotors 2 and 3) during operation and there is the need to consider the mounting positions and shapes of the blades (the stop blade 4 and the shutter blade 5), causing the problem that the design becomes complicated. In particular, when three or more blades are used and an attempt is made to further reduce the housing area of the blades in a fully opened state, the above problem becomes severe.